Three types of distantly related plants evolved to become carnivorous, but they each took their own independent route to develop these similar traits, a new study found.
Australian (Cephalotus follicularis), Asian (Nepenthes alata) and American (Sarracenia purpurea) pitcher plants all share biological features that enable them to devour insects – including a cupped leaf with slippery interior that prevents prey from escaping, and digestive fluids that break down they prey’s flesh and exoskeleton.
While these traits were first discovered in 1992, how each of the plants developed them remained unknown, until now.
Victor A. Albert, biologist at the University of Buffalo who also participated in the 1992 study, along with a team of colleagues, analyzed the entire genome of C. follucularis and found that at some point in the plant’s history, its proteins that respond to stressors and initiate self-defense mechanisms repurposed themselves into digestive enzymes that help them consume insects today.
C. follicularis forms both carnivorous and non-carnivorous leaves, which according to the team, provided a unique opportunity to study the origin of the plant’s carnivory.
The team also analyzed digestive fluid proteins from Asian and American pitcher plants and observed similar enzyme transformations.
As the study pointed out, each carnivorous plant lineage split from a common ancestor more than 100 million years ago, but they still all managed to repurpose their genes for similar functions. C. follicularis is related to the starfruit, Nepenthes alata is a relative of buckwheat and Sarracenia purpurea is related to kiwifruit.
The enzymes identified include basic chitinase, which breaks down a major component of insects’ hard, exterior shells, and purple acid phosphatase, which enables the plants to soak up phosphorus from their prey.
The findings are an example of convergent evolution, which is when unrelated species evolve independently to acquire similar traits, according to the authors. The results also hint that for plants, the evolutionary routes to carnivory may be few and far between.
"It suggests that there are only limited pathways for becoming a carnivorous plant," said Albert. "These plants have a genetic tool kit, and they're trying to come up with an answer to the problem of how to become carnivorous. And in the end, they all come up with the same solution."
"Carnivorous plants often live in nutrient-poor environments, so the ability to trap and digest animals can be indispensable given the dearth of other sources of nourishment," added co-author Kenji Fukushima, of the National Institute for Basic Biology in Japan.
The study was published in Nature Ecology & Evolution.